1. Field of the Invention
The present invention relates to a technical field of a lens barrel and an imaging apparatus, and particularly to a technical field in which a nut member made of a metal material is separated from a lens holder in a non-drive mode to improve resistance to impact.
2. Description of the Related Art
Any imaging apparatus, such as a video camera and a still camera, includes a lens barrel having an imaging capability. In recent years, a variety of electronic apparatus, such as mobile phones, personal computers, and PDAs (Personal Digital Assistants), have been used in an increasing number of applications, and some of such electronic apparatus include a built-in lens barrel. Therefore, mobile phones, personal computers, PDAs, and other electronic apparatus including such a built-in lens barrel are also used as imaging apparatus for capturing images.
Some of such lens barrels have a configuration in which an outer enclosure houses a fixed lens, such as an objective lens, a movable unit including movable lenses, such as a focus lens and a zoom lens, an imaging device that converts an image light acquired through the fixed lens and the movable lenses into an image signal, and other components.
Some of such lens barrels have a configuration in which a movable unit can be moved in the optical axis direction by a driving mechanism having a lead screw (see JP-A-08-95143, for example). The drive mechanism includes a drive motor and a lead screw rotated by the drive motor.
Some of the lens barrels described above use a rigid nut member made of a metal material as a nut in order to prevent so-called tooth chipping, which results in a shift in the position of the nut that threadably engages the lead screw, or so-called tooth scraping, in which the threaded groove of the nut is scraped, when an impact is applied.
In particular, since a mobile imaging apparatus is prone to receive an external impact, the tooth chipping and tooth scraping described above may degrade the reliability of the operation of the movable unit. To address the problem, it is desirable to use a nut member made of a metal material.
In the movable unit, a lens holder is supported by a guide shaft in such a way that the lens holder can slide in the optical axis direction, and a nut member threadably engages a lead screw. The nut member is then connected to the lens holder. An urging spring applies an urging force to the lens holder in the direction in which the lend holder is pressed against the nut member in order to reduce backlash between the nut member and the lead screw in the axial direction of the lead screw.
Therefore, the lens holder in the movable unit is typically pressed against the nut member by the urging spring.
The reduction in backlash between the nut member and the lead screw is necessary to ensure good positional accuracy when the movable unit moves in the optical axis direction in a drive mode in which an image is ready to be captured when a power supply is turned on.